1. Field of the Invention
The present invention relates, in general, to a system for preventing off-tracking of relatively long power driven articulated ground vehicles of the type having a center frame and leading and trailing steerable wheeled supports pivotally connected thereto at the opposite ends of the center frame; and, more particularly, to an automatic steering control or guidance system including provisions for: (i) continuously measuring a parameter indicative of the distance traveled by the vehicle; (ii) continuously measuring the leading angle .alpha..sub.1 between the longitudinal centerlines passing through the center frame and the leading wheeled support--which may take the form of a controlled tractor (controlled either automatically or manually by an operator)--to produce a first signal representative of the leading angle .alpha..sub.1 ; (iii) processing the first signal representative of the leading angle .alpha..sub.1 as a function of distance traveled to produce a lagged or delayed signal representative of the time average of the leading angle .alpha..sub.1 as the vehicle traverses linear and/or curvilinear paths; (iv) measuring the trailing angle .alpha..sub.2 between the longitudinal centerlines passing through the center frame and the trailing wheeled support to produce a second signal representative of the trailing angle .alpha..sub.2 ; (v) comparing the second signal representative of the trailing angle .alpha..sub.2 with the delayed first signal representative of the time average of the leading angle .alpha..sub.1 so as to produce a third signal representative of the angular difference between the trailing angle .alpha..sub.2 and the time average of the leading angle .alpha..sub.1 ; and (vi) utilizing the third signal to automatically control the steering angle .beta. of the trailing support so as to maintain the trailing angle .alpha..sub.2 substantially equal to the time average of the leading angle .alpha..sub.1, thus insuring that the trailing support travels over substantially the same path as the leading support as the articulated ground vehicle traverses a prescribed path of movement. In the illustrative form of the invention, the leading and trailing wheeled supports take the form of oppositely directed tractors each employing its own motive power system, each having steerable wheels, and each capable of functioning as a lead vehicle--i.e., the articulated vehicle is capable of being driven in a forward or reverse operational mode--yet, wherein the vehicle dynamics of the trailing tractor are slaved to the vehicle dynamics of the operator controlled leading tractor with active steering of the trailing tractor being delayed by a distance related interval of time represented by the time average of the leading angle .alpha..sub.1.
The present invention has been developed and is herein described in connection with the "MX Missile System"; and, is principally intended for use in transporting relatively long and heavy missiles along circuitous roadways between a multiplicity of irregularly spaced storage and launching sites. As such, the articulated vehicle to be described is extremely large; and, its intended use in transporting missiles from point-to-point in remote isolated areas of the country presents relatively unique problems in terms of accurate tracking of the trailing end of the articulated vehicle with respect to the leading end, manpower requirements, and other operating conditions peculiar to this proposed defensive missile system. However, while the invention finds particularly advantageous use with immense articulated vehicles of the type necessary to move such defensive missiles, it is not believed to be limited strictly to application to missile transport; but, rather, it is believed that the invention will find equally advantageous use with other types of long articulated ground vehicles requiring both leading and trailing steerable wheels such, merely by way of example, as long fire engines, long articulated buses, long tractor/trailers, etc.
2. Prior Art
Because of the size of the exemplary articulated vehicle to be described herein and the complete absence of comparable vehicles in the prior art, the problems encountered--for example, in maintaining proper tracking of the trailing tractor, and preventing disorientation and/or nausea inherent with operators required to man and steer a trailing tractor moving backwards--are problems which are not believed to have been experienced prior to the advent of the present invention. More specifically, there are no known prior art approaches to the problem of controlling tracking of long articulated ground vehicles of the type having a central load-supporting frame and a pair of oppositely directed tractors pivotally connected to and supporting the central frame at the opposite ends thereof, with one of the tractors being either manned for operator control or being automatically controlled, and the other of the tractors being unmanned and slaved to the vehicle dynamics of the system during normal over-the-road operation. However, numerous devices have been described in the prior art comprising mechanical and/or electromechanical designs relating to vehicle steering and propulsion systems; but, in general, such systems are not related to automatic steering of one end of an articulated vehicle with respect to the other end thereof, nor do they recognize the advantages to be achieved by steering an unmanned tractor in response to differences between: (i) a first delayed signal representative of the time average of the leading angle defined by longitudinal centerlines passing through the central frame and the leading tractor; and (ii) a second signal representative of the trailing angle defined by longitudinal centerlines passing through the central frame and the trailing tractor.
One patent of general interest is U.S. Pat. No. 2,419,812-Bedford which describes a servo control mechanism for compensating for the effects of friction upon the accuracy or performance of electrical servo systems or follow-up systems. However, the Bedford patent relates specifically to a motor control system as contrasted with a vehicle steering system; and, does not disclose or suggest an angle lag control steering system for long articulated ground vehicles.
Another prior art patent of general interest is Chu et al U.S. Pat. No. 2,996,137 which relates to a radar guidance and computer controlled automatic system for providing speed and directional control of land vehicles. This patent does not, however, disclose any means for automatically tracking one end of a vehicle with respect to the other end thereof.
Kohls U.S. Pat. No. 3,498,403 disclose a vehicle guidance control system employing active buried guide wires embedded along the desired path of vehicular movement; and, wherein vehicles are provided with an automatic steering mechanism for guiding the vehicle along the path defined by the buried guide wire with automatic steering compensations being made for deviations from the guide path. Again, the Kohls patent does not envision a steering guidance system wherein the steering controls for the trailing end of a long articulated ground vehicle are slaved to the vehicle dynamics of, for example, a manned or automatically controlled tractor at the leading end of the vehicle, with control signals generated at the leading end of the vehicle being lagged as a function of distance traveled.